I brought up the subject of allowing newtypes in kind # (or even in any kind that ends in * or # after a chain of ->'s to get more powerful Coercible instances) at ICFP this year and Simon seemed to think it'd be a pretty straightforward modification to the typechecker.
I confess, he's likely waiting for me to actually sit down and give the idea a nice writeup. ;) This would be good for many things, especially when it comes to improving the type safety of various custom c-- tricks. -Edward On Sun, Dec 20, 2015 at 2:14 PM, Ömer Sinan Ağacan <omeraga...@gmail.com> wrote: > I have another related question: What about allowing primitive types > in newtypes? > > λ:4> newtype Blah1 = Blah1 Int > λ:5> newtype Blah2 = Blah2 Int# > > <interactive>:5:23: error: > • Expecting a lifted type, but ‘Int#’ is unlifted > • In the type ‘Int#’ > In the definition of data constructor ‘Blah2’ > In the newtype declaration for ‘Blah2’ > > Ideally second definition should be OK, and kind of Blah2 should be #. Is > this > too hard to do? > > 2015-12-16 17:22 GMT-05:00 Richard Eisenberg <e...@cis.upenn.edu>: > > > > On Dec 16, 2015, at 2:06 PM, Ömer Sinan Ağacan <omeraga...@gmail.com> > wrote: > >> > >> In any case, this is not that big deal. When I read the code I thought > this > >> should be a trivial change but apparently it's not. > > > > No, it's not. Your example (`f :: (Int#, b) -> b`) still has an unboxed > thing in a boxed tuple. Boxed tuples simply can't (currently) hold unboxed > things. And changing that is far from trivial. It's not the polymorphism > that's the problem -- it's the unboxed thing in a boxed tuple. > > > > Richard > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >
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